1. Field of the Invention
The present invention relates to a method and apparatus for supplying slurries used in a chemical mechanical polishing (CMP) process for semiconductor device manufacture, and more particularly, to a slurry supplying method and apparatus which can perform a pre-treatment for de-agglomerating agglomerated abrasive particles within the slurry into particles of a sufficiently small size, so as not to damage the polished surface of a wafer during the CMP process.
2. Description of the Related Art
As miniaturization, high integration, and multi-layer metallization of semiconductor devices proceed, fine-pattern formation techniques are required. This results in more complicated surface configuration of semiconductor devices, and, in addition, the step difference on interlayer films becomes increasingly larger. Thus, a CMP process is used as a planarization technique for removing the step difference of a specific film formed on a substrate. In a CMP process, a slurry is provided on the surface of a thin film pattern on a wafer, and the surface of the thin film is in contact with a polishing pad. Then, the surface of the thin film chemically reacts with the slurry and the polishing pad is rotated, thereby physically polishing irregularities on the surface of the thin film to planarize the thin film.
In general, a CMP process is a technique of global planarization that cannot be achieved by the existing spin-on-glass (SOG) technique, or by etchback, thereby obtaining the polished surface having a good planarity. However, if a CMP process is carried out using slurries provided by a conventional method, a large amount of micro-scratch defects occur on the polished wafer surface. The micro scratch defects, which have been demonstrated to be created by abrasive particle clumps having a relatively large particle diameter among abrasive particles contained within a slurry, may result in electrical shorts, or bridge effects, in a wiring substrate for semiconductor integrated circuits.
Usually, abrasive particles contained in a slurry are comprised of primary particles having a diameter of about 130-170 nm. However, since abrasive particles tend to be agglomerated among unit particles that are suspended within the slurry, secondary particles having a relatively large diameter are thereby formed in clumps. The tendency of agglomeration of abrasive particles within the slurry is especially prominent when the slurry does not flow, but is instead stagnant. The range of sizes of the clumps formed by agglomeration of abrasive particles tends to lie from about 0.1 to about 30 xcexcm, depending on the size of the primary particles within the abrasive particles. In particular, when a ceria-based slurry using cerium oxide particles (hereinafter referred to as xe2x80x9cceria slurryxe2x80x9d) is used, exceeding merely 1 xcexcm in the average size of the particles within the slurry has been known to produce a large quantity of micro-scratch defects on the polished surfaces of weak films such as chemical vapor deposition (CVD) films formed by low temperature chemical reaction, or organic or inorganic deposition films.
For addressing this issue, U.S. Pat. No. 5,895,550 discloses a method in which ultrasonic transducers are connected in-line with a slurry dispense line. This method employs a single-pass system in which the slurry flows through the ultrasonic transducer connected to the slurry dispense line just prior to dispensing on the polishing pad. In a configuration that uses the ultrasonic transducers by a single-pass system, it is difficult to uniformly and effectively transmit acoustic energy of sufficient strength to de-agglomerate agglomerated abrasive particles within the slurry into primary particles.
Furthermore, since the ceria slurry is typically extracted from a highly impure mineral and obtained through processes such as high purification and granulation unlike a colloidal silica-based slurry, it inevitably contains a small amount of impurities. For this reason, the ceria slurry can contain relatively large, abrasive, particle clumps that cannot be reduced by application of acoustic energy. Clumps formed by simple agglomeration of primary particles can readily be broken apart by supplying acoustic energy; however large-sized abrasive particle clumps produced by other causes are not reducible through the application of acoustic energy.
To address the aforementioned limitations, it is a first objective of the present invention to provide a slurry supplying method which is capable of minimizing the abrasive particle size of a slurry used in a chemical mechanical polishing (CMP) process so as to avoid the generation of micro-scratch defects on the polished surface of a wafer.
It is a second objective of the present invention to provide a slurry supplying apparatus for pre-processing of a slurry for preparing the slurry to have a minimized abrasive particle size for application in a CMP process.
Accordingly, to achieve the first objective, in a slurry supplying method according to the invention, acoustic energy is applied to a slurry for a chemical mechanical polishing (CMP) process to de-agglomerate agglomerated abrasive particles within the slurry. Then, oversized abrasive particles having a diameter greater than a reference size are filtered out from the slurry to which the acoustic energy is applied. Next, the slurry is circulated while continuing to apply acoustic energy continuing to filter for a predetermined time. The slurry subjected to the circulating step is supplied onto a polishing pad of a CMP equipment.
The acoustic energy source applies acoustic energy to the slurry held within a tank. Preferably, the acoustic energy source at least a portion of which is immersed in the slurry applies acoustic energy to the slurry. The acoustic energy source may apply acoustic energy to the slurry from the bottom or the sidewalls of the tank. In this case, an ultrasonic transducer may be used as the acoustic energy source.
The slurry may comprise ceria slurry, silica slurry, or alumina slurry.
To achieve the second objective, the present invention provides a slurry supplying apparatus including a tank for holding a slurry to be used in a chemical mechanical polishing (CMP) process, acoustic energy sources for applying acoustic energy to the slurry held within the tank, a slurry circulating line for circulating the slurry drawn out of the tank, which is connected to the tank, a filter for filtering out abrasive particle clumps having a diameter greater than a reference size from the slurry, which is disposed in the slurry circulating line, and a slurry supplying line for supplying the slurry from the slurry circulating line to a CMP equipment.
The acoustic energy sources may selectively include a first acoustic energy source at least a portion of which is immersed in the slurry held within the tank, a second acoustic energy source for applying acoustic energy to the slurry from the bottom of the tank, and a third acoustic energy source for applying acoustic energy to the slurry from the sidewalls of the tank.
The slurry circulating line includes a slurry discharge line connected to an outlet of the tank and a slurry collecting line connected to an inlet of the tank. The filter may be disposed in the slurry discharge line or the slurry collecting line. The slurry circulating line may further include a bypass line for detouring the filter so that the slurry can be circulated without passing through the filter.
The method of supplying a slurry according to the present invention not only applies acoustic energy to a slurry through all regions within a slurry source sink, but also suppresses re-agglomeration of abrasive particles caused by slurry stagnation since the slurry is continuously maintained not in a stagnant state, but rather in a fluid state.
Furthermore, since there is no danger that agglomerated abrasive particles or oversize abrasive particles will exist within a slurry provided through the slurry supplying apparatus according to the present invention, the apparatus can suppress production of micro-scratches which may cause defects in a semiconductor device on the polished surface of a wafer during a CMP process.